1. Technical Field
The present disclosure relates to a switchable type display device, and more particularly, to a display device switchable between a 2D image and a 3D image including a film type lens panel using a nano liquid crystal.
2. Discussion of the Related Art
Recently, a switchable type display device which selectively displays a two-dimensional (2D) image or a three-dimensional (3D) image has been suggested. In the switchable type display device, a liquid crystal layer between a concave lens layer and a substrate selectively functions as a lens according to application of an electric field using an optical anisotropy of a liquid crystal molecule.
FIGS. 1A and 1B are cross-sectional views showing a light path of a switchable type display device in a 2D mode and a 3D mode, respectively, according to the related art.
In FIGS. 1A and 1B, a switchable type display device 10 includes a display panel 20 and a lens panel 30. The display panel 20 displays an image using a plurality of pixels including first to third pixels P1 to P3. The light emitted from the display panel 20 may have a polarized state along a predetermined direction while passing through a polarizing plate 44. For example, the light may have a polarized state of a direction perpendicular to a cross-sectional surface.
The lens panel 30 is disposed over the display panel 20 and selectively refracts or transmits a light emitted from the display panel 20. The lens panel 30 includes first and second substrates 40 and 50 facing and spaced apart from each other and a liquid crystal layer 60 between the first and second substrates 40 and 50. First and second electrodes 42 and 52 are formed on inner surfaces of the first and second substrates 40 and 50, respectively. In addition, a transparent concave lens layer 54 is formed on the second electrode 52.
The concave lens layer 54 has a plurality of concave portions on a bottom surface thereof and each of the plurality of concave portions has a half-cylindrical shape. The liquid crystal layer 60 is disposed in the plurality of concave portions between the concave lens layer 54 and the first electrode 42.
The liquid crystal layer 60 includes a plurality of liquid crystal molecules 60a and each of the plurality of liquid crystal molecules 60a has a birefringence property which shows an ordinary refractive index (no) or an extraordinary refractive index (ne) according to a direction of a light. In the liquid crystal layer 60, the plurality of liquid crystal molecules 60a may be horizontally aligned such that a long axis of the liquid crystal molecule 60a is perpendicular to the cross-sectional surface. In addition, the concave lens layer 54 may include a material having a refractive index the same as the ordinary refractive index (no) of each liquid crystal molecule 60a. 
The switchable type display device 10 selectively displays a 2D image or a 3D image according to an alignment state of the liquid crystal layer 60. In a 2D mode where a 2D image is displayed, as shown in FIG. 1A, a voltage is applied to the first and second electrodes 42 and 52 (ON) and an electric field is generated between the first and second electrodes 42 and 52. As a result, the liquid crystal layer 60 is re-aligned such that a long axis of the liquid crystal molecule 60a is parallel to the direction of the electric field.
The light that have passed through the polarizing plate 44 has a polarized state of a direction perpendicular to the cross-sectional surface and parallel to a short axis of the liquid crystal molecule 60a and is applied to the liquid crystal layer 60 having the ordinary refractive index (no). As a result, the light is not subject to a difference in refractive index at an interface between the liquid crystal layer 60 having the ordinary refractive index (no) and the concave lens layer 54 having the ordinary refractive index (no). Therefore, the light having the polarized state of a direction perpendicular to the cross-sectional surface intactly passes through the lens panel 30 without refraction and the switchable type display device 10 displays a 2D image.
In a 3D mode where a 3D image is displayed, as shown in FIG. 1B, a voltage is not applied to the first and second electrodes 42 and 52 (OFF) and an electric field is not generated between the first and second electrodes 42 and 52. As a result, the liquid crystal layer 60 keeps the initial alignment state where a long axis of the liquid crystal molecule 60a is perpendicular to the cross-sectional surface.
The light that have passed through the polarizing plate 44 has a polarized state of a direction perpendicular to the cross-sectional surface and parallel to a long axis of the liquid crystal molecule 60a and feels that the liquid crystal layer 60 has the extraordinary refractive index (ne). As a result, the light is subject to a difference in refractive index at an interface between the liquid crystal layer 60 having the extraordinary refractive index (ne) and the concave lens layer 54 having the ordinary refractive index (no). Therefore, the light having the polarized state of a direction perpendicular to the cross-sectional surface is refracted while passing through the lens panel 30 and the switchable type display device 10 displays a 3D image.
In the switchable type display device 10 according to the related art, since the liquid crystal layer 60 is formed by filling a space between the first and second substrates 40 and 50 with the liquid crystal molecules 60a of a fluid state, a thickness of the switchable type display device 10 increases and there is a limitation to fabricate the lens panel 30 as a film type. Accordingly, fabrication cost of the switchable type display device 10 increases. In addition, since the liquid crystal molecules 60a of the liquid crystal layer 60 sags and a cell gap is not kept uniformly due to gravitation even after the lens panel 30 is fabricated, a switchable property between the 2D image and the 3D image is deteriorated.